Theory for massive stars and understand how a black hole might be formed

A similar suggestion was made a few years later by the French scientist the
Marquis de Laplace, apparently independently of Michell. Interestingly
enough, he included it in only the first and second editions of his book, The

System of the World, and left it out of later editions; perhaps he decided that it
was a crazy idea. In fact, it is not really consistent to treat light like cannonballs in Newton's theory of gravity because the speed of light is fixed. A cannonball fired upward from the Earth will be slowed down by gravity and will
eventually stop and fall back. A photon, however, must continue upward at a
constant speed. How, then, can Newtonian gravity affect light? A consistent
theory of how gravity affects light did not come until Einstein proposed general relativity in 1915; and even then it was a long time before the implications of the theory for massive stars were worked out.
To understand how a black hole might be formed, we first need an understanding of the life cycle of a star. A star is formed when a large amount of gas, mostly hydrogen, starts to collapse in on itself due to its gravitational attraction. As
it contracts, the atoms of the gas collide with each other more and more frequently and at greater and greater speeds—the gas heats up. Eventually the gas
will be so hot that when the hydrogen atoms collide they no longer bounce off
each other but instead merge with each other to form helium atoms. The heat
released in this reaction, which is like a controlled hydrogen bomb, is what
makes the stars shine. This additional heat also increases the pressure of the
gas until it is sufficient to balance the gravitational attraction, and the gas
stops contracting. It is a bit like a balloon where there is a balance between the
pressure of the air inside, which is trying to make the balloon expand, and the
tension in the rubber, which is trying to make the balloon smaller.
The stars will remain stable like this for a long time, with the heat from the
nuclear reactions balancing the gravitational attraction. Eventually, however,
the star will run out of its hydrogen and other nuclear fuels. And paradoxically, the more fuel a star starts off with, the sooner it runs out. This is because
the more massive the star is, the hotter it needs to be to balance its gravitational attraction. And the hotter it is, the faster it will use up its fuel. Our sun
has probably got enough fuel for another five thousand million years or so, but
more massive stars can use up their fuel in as little as one hundred million
years, much less than the age of the universe. When the star runs out of fuel,
it will start to cool off and so to contract. What might happen to it then was
only first understood at the end of the 1920s.
In 1928 an Indian graduate student named Subrahmanyan Chandrasekhar set
sail for England to study at Cambridge with the British astronomer Sir Arthur
Eddington. Eddington was an expert on general relativity. There is a story that
a journalist told Eddington in the early 1920s that he had heard there were
only three people in the world who understood general relativity. Eddington
replied, “I am trying to think who the third person is.”